IMPROVING THE TECHNIQUE FOR MEASURING COORDINATES OF THE STRING PLUMB-LINES IN HYDRAULIC STRUCTURES

摘要

Direct and inverted string plumb-lines are one of the most widely used techniques for geodetic control of hydraulic structures (HSs). Currently, X-Y coordinate string transducers (XYST) are used to monitor the string deflection in HS control―by way of example, those designed at the Novosibirsk Institute of Applied Geodesy (Novosibirsk, Russia). Basic specifications for XYSTs are: XYST 20/20-type, displacement measurement range not less than 20 x 20 mm; XYST 100/20―not less than 100 x 20 mm; overall X- and Y-tolerance, not greater than 0.1 mm; string input action―sinusoidal current with a frequency of 62.5 +- 0.05 kHz; effective current 70 +- 20 mA; output signal― voltage with an amplitude of 0 - 10 mV (62.5 +- 0.05 kHz), depending on the input signal; ambient temperature, 5 - 30℃; relative humidity, 80- 100%. The XYST transform function is given as a tabular algebraic surface stored in a database system for each XYST. A shortcoming of this technique is that XYST must be periodically checked for calibration using a special optical test bench; with a large number XYSTs employed (for example, in a hydropower plant, it may be 700 or even greater), this will require additional effort from personnel, with no guarantee that all measurements are free of sporadic errors due to engineering factors.